1. Field of the Invention
The invention relates to an automatic pipetting and handling machine for microtitration plates with a, permeable base, e.g. filter of plates or membrain bottom plates.
2. Description of the Prior Art
Microtitration plates with permeable bases have been in use in screening laboratories for a number of years. There is a wide range of products, which differ with regard to the type of bases and therefore with regard to their interaction with the liquid media situated in the so-called wells. The handling of liquid using these filter plates can essentially be described by means of the following steps: filling the wells with liquid from above and, after a reaction time, sucking the liquid downward through the filter layer. The filling step is carried out using conventional handheld pipettes or pipetting robots and does not differ from the procedure used for conventional microtitration plates. The suction step, or emptying of the wells, is not carried out via the openings of the latter, but rather, at so-called suction stations, through the base of the wells. The structure of these suction stations is essentially as follows. The filter plate is placed onto a suction tray, which has a surrounding rubber seal in the area where the edge of the filter plate rests. On the bottom of the suction tray, there is an opening which is connected to a vacuum device. This vacuum device generally comprises a Woulff bottle for separating off the liquid, an aeration valve and a vacuum pump. When working manually, the procedure is as follows. The filled filter plate is placed and pressed onto the suction tray, and at the same time a vacuum is applied to the suction tray via its opening. An important factor here, depending on the design of the filter plate, is whether the vacuum is built up slowly by a pump being switched on or is brought about suddenly by connecting the vacuum with a nominal pressure.
The automatic procedure is similar to the manual sequence, in that either the filter plate is filled by a pipetting robot directly at the suction station, or, if the pipetting robot has a plate-gripping mechanism, it pipettes the plates and then deposits them on the suction device for the suction period. In the latter case, it is possible for the gripper arm to press the filter plate onto the suction station, in order to enable it to be sucked on securely so that the vacuum can be built up. Naturally, the forces which can be applied to do this are low. In the first of the two cases, it is still possible to apply the filter plate with a vacuum shock.
The throughput of such appliances is limited by the number of needles available for liquid handling; known systems are fitted with one to eight needles.
Furthermore, systems with an integrated gripper are relatively large and slow. The size of such an appliance is important, since it is often necessary to carry out the process described above in a workbench which is protected by means of a laminar air flow.
The invention is based object of providing a compact arrangement with which filter plates can be removed from a storage system, pipetted, sucked empty and stored automatically, in an efficient time and with a high throughput.
According to the invention, this object is achieved by an automatic pipetting and handling machine for microtitration plates with a permeable base, comprising a carriage which can be displaced on a horizontal guide path. The carriage has a dispenser stacking section, a storage stacking section, an automatic pipetting machine and a pressure station arranged along the guide path. The carriage also has a suction station.